Conference circuits for digital communication systems are well known in the art. Such conference circuits typically employ techniques similar to either the summing technique shown by, e.g., U.S. Pat. No. 4,416,007, to D. D. Huizinga, et al., or to the loudest speaker technique shown by, e.g., U.S. Pat. No. 3,699,264, to S. G. Pitroda, et al.
The summing technique employed by the Huizinga conferencing arrangement requires a plurality of adders, including a multiple input adder, and subtractors. A known conference circuit employing the loudest speaker technique has a digital threshold detector to determine the presence of the loudest speaker. Such a circuit is shown, e.g., by commonly assigned copending U.S. patent application Ser. No. 427,970 filed Sept. 29, 1982 of B. D. Shuh, entitled "PCM Conference Circuit" and incorporated herein by reference. The conference circuit then connects this source to all other lines in the conference while at the same time deleting the signal to the line determined to be the source of the loudest speaker. The main difficulty with this circuit relates to the operation of the loudest speaker threshold detector. The circuit operates in a satisfactory manner when the background noise on all lines in the conference is low and the levels are equal. However, when the noise level on one or more lines increases, one line can dominate others, especially if some of the lines are low level trunk circuits. Also, the detector may switch between noisy lines producing an annoying chopping effect. The circuit is also limited in the total number of multi-line conferences which can be provided simultaneously.